Electron inhibited electrode member and method of making same



T970 '0. G. KoP Plus 3,529,203-

ELECTRON INHIBITED ELECTRODE MEMBER AND METHOD OF MAKING SAME Filed Jan. 25, 1968 2 Sheets-Sheet l FiG-i UVVENTUR OTTO G. KOPPIUS Sept. 15, 1970 I o. G. KOPPIUS ,2

ELECTRON INHIBITED ELECTRODE MEMBER AND METHOD OF MAKING SAME Filed Jan.- 25, 1968 2 SheetsShe9t 2 1/ 82 .6 f 82 iv vi 4-|4D I I6 1 I00 F lG-5 F IG-6 l/VVf/VTOR OTTO e. KOPPIUS United States Patent Office Patented Sept. 15, 1970 3 529 203 ELECTRON INHIBITED ELECTRODE MEMBER AND METHOD OF MAKING SAME Otto G. Koppius, Florence, Ky. (280 Lakeshore Drive, Clermont, Fla. 32711) Filed Jan. 25, 1968, Ser. No. 700,411 Int. Cl. H01j 1/20, 19/14 U.S. Cl. 313-337 21 Claims ABSTRACT OF THE DISCLOSURE This invention relates generally to a method of making, and to electrodes per se which in use are in contact with or adjacent to dispenser cathode structures for precisely limiting or defining the effective emissive area of the cathode.

Specifically the invention relates to emission inhibiting coatings applied to such electrodes, to such electrodes per se, and to a method of making such electrodes.

A primary object of the invention is to provide an electrode of carburizable refractory metal having an outer surface in the form of a barium oxide reactive alloy of the refractory metal wherein cetain of said alloyed surfaces are carburized for rendering them non-emissive in the presence of barium oxide at temperatures in excess of 850 C.

The prior art method of inhibiting electron emission from electrodes on or in the vicinity of the cathode has been to provide a layer of molybdenum and/ or tungsten carbide on the surface and while the prior art process results in a satisfactory inhibiting surface for many applications, it suffers from the serious deficiency that electrodes which are made from molybdenum and then carburized grow in size and become off tolerance.

It is accordingly an object of this invention to provide an improved inhibiting coating that has negligible growth when the electrode parts are carburized.

Another object of the invention is to provide a simple, foolproof and inexpensive technique of forming such a coating.

The foregoing objects are attained by the means described herein and disclosed in the accompanying drawings wherein:

FIG. 1 is a cross-sectional view of a hollow beam cathode assembly embodying the teachings of the present invention.

FIGS. 2 and 3 are sectional views of the coated electrode of FIG. 1 per se in the process of manufacture.

FIG. 4 is a sectional view of a magnetron sleeve cathode assembly with electrodes embodying the teachings of the present invention.

FIGS. 5 and 6 are sectional views illustrating steps in the process of producing the coated electrodes of the assembly of FIG. 4.

With reference now to FIGS. 1 and 4 the numerals 10 denote generally a support of refractory metal, the numerals 12, a cathode having emissive surfaces; the numerals 14, electrodes having non-emissive surfaces 16, and the numerals 18, heating filaments.

With particular reference now to FIG. 1, it will be noted that I have disclosed a hollow beam cathode assembly in which one end of a tubular support member 10 of refractory metal is closed by a cathode 12 in the form of a circular disc having a pair of parallel, flat laterally spaced inner and outer surfaces 20 and 22 respectively, a side surface 24 and a circular bore extending axially therethrough defined by axial walls 26 and 30 and transverse wall 28.

The cathode is made in any suitable manner, not germane to the present invention, whereby to have surfaces which are adapted to be rendered emissive in the presence of barium oxide at temperatures in excess of 850 C., such as developed by heating filament 18.

The electrode 14 is substantially cylindrical having a lower plug-like portion '40 dimensioned to be snugly received within cylindrical bore-portion 30 of the cathode for disposing surface 42 of the electrode in contacting relationship with the surface of transverse Wall 28 of said bore.

Axial or side surface 44 of the electrode is dimensioned whereby to be in closely spaced relationship with the surface of axial wall 26 of the bore of the electrode, as illustrated.

For the proper functioning of-the cathode assembly of FIG. 1 in a microwave discharge device the position of electrode 14 relative to cathode 12 is extremely critical since the non-emissive surfaces of the electrode act as a beam forming electrode in conjunction with the emissive surfaces of the cathode.

The close tolerance involved will be appreciated when one realizes that the outside diameter of the cathode 12 in many cases is less than .060 inch, the width of its periphery, viz annular surface 22, is about .010 inch and that the dimensions of the electrode must be held to less than a half-thousandth of an inch.

In accordance with the present invention electrode 14 is formed of a carburizable refractory metal having a melting point of above 1800 C., which is formed to required dimension and tolerances by any suitable process such as machining, rolling, drawing or the like.

After being formed to final dimensions, as above noted, the entire outer surface of the electrode is provided with a coating of a barium oxide reactive material by placing the electrode in a vacuum chamber having filaments and electrodes arranged to evaporate an .0001 inch to .010 inch layer of a barium oxide reactive material onto the entire outer surface of the electrode. Then the excess coating material is removed simultaneously with the formation of an alloy of the layer material with the refractory metal of the electrode by placing the coated electrode in a vacuum furnace and gradually increasing the temperature to 1800 C. The coated electrode is maintained at said temperature for a period of time sufficient to diffuse the barium oxide reactive material into the surfaces of the electrode to form an alloy therewith. Uniformly satisfactory results have been obtained when the 1800 C. temperature is maintained for 10 minutes after which the electrode is allowed to cool in a vacuum to room temperature.

In so far as it can be determined, the thus formed alloyed surfaces of the electrode have substantially the same dimensions 'which the electrode had before the barium oxide reactive material was deposited onto it, however, the overall appearance of the electrode differs by reason of its alloyed surfaces.

Those surfaces of the electrode which are to be rendered non-emissive are then carburized. This may be effected by heating those surfaces in contact with carbon in a vacuum furnace for a period of time sufiicient to completely carburize those of the alloyed surfaces which are in direct contact with carbon.

With particular reference now to FIGS. 2 and 3 the numeral 50 denotes a carbon block having a socket pro- 3 vided therein dimensioned to snugly receive those of the alloyed electrode which are to be rendered non-emissive. Uniformly satisfactory results have been obtained in those instances wherein a unit as illustrated in FIG. 2 is placed in a vacuum furnace and heated to l500 C. for a period of 10 minutes.

In FIG. 3 the stippled surfaces indicated by the numeral 16 represent the carburized surfaces of the barium oxide reactive alloy of the refractory metal.

The electrode of FIG. 3 is then associated with the cathode 12 as in FIG. 1 and permanently affixed thereto by brazing or staking as at 60'.

As earlier noted, cathode 12 is fabricated of material which will be rendered emissive in the presence of barium oxide at temperatures exceeding 850 C., however, the presence of electrode 14 effectively restricts the effective emissive surface of the cathode in an annulus defined by the width of upper surface 22.

With particular reference now to FIG. 4 I have disclosed the invention as applied to a magnetron-sleeve cathode assembly wherein the cathode 12 comprises a hollow sleeve having an outer surface 70, an inner surface 73 which is dimensioned to snugly engage the outer surface of support member 10; and end surfaces 72, 74 and 76 respectively.

The electrodes 14 are in the form of end hats which include a shorter mounting portion 80 and a longer shielding portion 82 disposed at right angles therewith. In FIG. 4 -I have illustrated four different types of electrodes, each of which embody the teachings of my invention, however, it should be clearly understood that in actual practice but one type of electrode structure will be used in connection with any particular magnetron sleeve cathode assembly.

The electrodes of FIGS. 4, and 6 are fabricated in the same manner as the electrode of FIG. 1, viz from a carburizable refractory metal capable of being rendered emissive in the presence of barium oxide at temperatures exceeding 850 C. and which is machined, rolled or drawn to required dimensions and tolerances. A layer of barium oxide reactive material is deposited onto the surfaces of the electrode after which the excess material is removed while other portions of the material are simultaneously diffused into the surface of the electrode to form an alloy with the refractory metal.

Thereafter those alloyed surfaces of the electrode which are to be rendered non-emissive are carburized, said carburized surfaces being indicated by stippling 16.

With particular reference now to FIG. 4 it will be noted that all of the surfaces of the electrode denoted by the numeral 14A have been carburized except surface 83 which is provided in contacting engagement with the outer surface of support member by any suitable means. It should be noted that the adjacent surface 84 of electrode 14A is spaced from end surface 72 of cathode 12 as illustrated.

Electrode 14B differs from 14A- solely in that surface 88 which contacts the outer surface of support member 10 has been carburized.

Electrode 14C is similar to 14A, however, surface 84 is maintained in spaced relationship with respect to end 76 of the cathode by means of a wire 90 which constitutes a positive spacer element which circumscrihes the support member 10.

Electrode 14D differs from those denoted by the designation 14A, 14B and 14C in that surface 100 of electrode 14D is disposed in contacting relationship with end surface 76 of the cathode 12.

With particular reference now to FIG. 5 it will be noted that the electrode 14D may be formed by providing the electrode with a carburized surface 16 after which the electrode is cut, such as by means of sawing along a line 102, for providing a clean metallic surface 100 on the electrode.

As used herein the term refractory metal or carburizable refractory metal refers to metals having a melting point above 1800 C., to wit, molybdenum, tungsten, tantalum and columbium.

The term barium oxide reactive material includes titanium and zirconium which are characterized in that the alloy of said metals formed with the refractory metal is very stable after said alloyed surface has been carburized and wherein said carburized alloyed surfaces are extremely reactive and non-emissive in the presence of barium oxide at temperatures exceeding 850 C.

It should be understood that various changes and modifications in the structural details of the device may be made within the scope of the appended claims without departing from the spirit of my invention.

What is claimed is:

1. A carburizable refractory metal electrode capable of being rendered emissive in the presence of barium oxide at temperatures exceeding 850 C. having an outer surface comprising a barium oxide reactive alloy of the refractory metal with certain said alloyed surfaces carburized, said carburized surfaces being non-emissive in the presence of barium oxide at said temperature.

2. An electrode comprising in combination: a support member of refractory metal, a cathode having emissive surfaces, means securing said cathode to said support member, an electrode having non-emissive surfaces and means securing said electrode relative to said cathode for restricting the emission of electrons from the cathode to certain predetermined surfaces thereof, and means securing said electrode relative to said cathode.

3. An electrode as called for in claim 2 wherein the non-emissive surfaces of the electrode are in spaced relationship with corresponding emissive surfaces of the cathode.

4. An electrode as called for in claim 2 wherein the electrode is formed of a carburizable refractory metal having a melting point of over 1800 C. wherein the outer surface of the electrode comprises a barium oxide reactive alloy of the refractory metal, and wherein those alloyed surfaces of the electrode which are non-emissive are carburized.

5. A process of providing a carburizable refractory metal electrode with non-emissive surfaces, which comprises the steps of:

(A) forming, to final dimensions, an electrode of a carburizable refractory metal;

(B) depositing a barium oxide reactive layer onto the surfaces of said electrode;

(C) removing excess layer material while simultaneously diffusing said material into the surface of the electrode to form an alloy with the refractory metal;

(D) carburizing those of the alloyed surfaces of the electrode which are to be non-emissive.

6. A process as set forth in claim 5 wherein the carburizable refractory metal has a melting point of above 1800 C.

7. A process as set forth in claim 5 wherein the carburizable refractory metal comprises molybdenum.

8. A process as set forth in claim 5 wherein the carburizable refractory metal comprises tungsten.

9. A process as set forth in claim 5 wherein the carburizable refractory metal comprises tantalum.

10. A process as set forth in claim 5 wherein the carburizable refractory metal comprises columbium.

11. The process as set forth in claim 5 wherein the barium oxide reactive layer constitutes titanium.

12. The process as set forth in claim 5 wherein the barium oxide reactive layer constitutes zirconium.

13. A process as set forth in claim 5 wherein the barium oxide reactive layer deposited onto the surface of the electrode is at least .0001" thick.

14. A process as set forth in claim 5 wherein the barium oxide reactive layer is deposited by evaporation onto the electrode.

15. A process as set forth in claim 5 wherein a barium oxide reactive layer of at least .0001 is deposited onto the electrode by heating the layer material to temperatures sufiicient to evaporate and deposit same onto the electrode.

16. A process as set forth in claim 5 wherein the elec trode coated with a barium oxide reactive layer is heated in a vacuum furnace for diffusing some of the layer material into the surface of the electrode for reacting therewith to form a barium oxide reactive alloy surface on the electrode while evaporating the balance of said layer material from said electrode.

17. A process as set forth in claim 16 wherein the electrode coated with a barium oxide reactive layer is heated in a vacuum furnace to '1800 C. until a barium oxide reactive alloy surface is provided on the electrode after which it is cooled in a vacuum to room temperature.

'18. The process as set forth in claim 17 wherein the 1800" C. temperature is maintained for approximately ten minutes.

19. A process as set forth in claim 5 wherein the dimensions of the alloyed surfaces of the electrode are substantially identical with those of the electrode before the barium oxide reactive layer was deposited onto the surface of the electrode.

20. A process as set forth in claim 5 wherein those UNITED STATES PATENTS 2,051,828 8/1936 Dester 3l3107 X 2,093,711 9/1937 Dallenbach 313334 2,158,845 5/1939 Ayer 313332 X 2,438,732 3/1948 Williams .v 313345 X 2,456,761 12/1948 Williams 313-44 5 2,636,856 4/195'3 Suggs et a1. 313- 352 X 2,764,511 9/1956 Iversen 313-345 X JOHN W. HUCKERT, Primary Examiner A. J. JAMES, Assistant Examiner US. Cl. X.R. 

